Modulational stability of plane waves in nonreturn-to-zero communications systems with dispersion management

Dispersion-managed optical transmission lines, with dispersion periodically switched between the normal and anomalous regimes, offer significantly better performance than transmission lines with constant dispersion by reducing the dispersion penalty and spectral broadening owing to self-phase modulation. We analyze the evolution of plane waves in a dispersion-managed transmission line, using Floquet theory, and show them to be modulationally stable, provided that the average dispersion is zero or negative (normal dispersion) and that the switching is fast enough, and to be unstable when anomalous dispersion dominates. These results indicate that the transition regions between 1's and 0's are primarily responsible for pulse deformations.